BTK and B-cell chronic lymphocytic leukemia: The outcome of CLL patients who are refractory or relapsed to immunochemotherapy changed with the development of novel agents inhibiting BCR signaling, e.g., Bruton’s tyrosine kinase (BTK) inhibitor ibrutinib and the phosphoinositide 3-kinase (PI3K) delta inhibitor idelalisib [4,13,14].